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Antigravity posture for analysis of motor unit recruitment: The “45 degree test”
Author(s) -
Petajan Jack H.
Publication year - 1990
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880130412
Subject(s) - motor unit , biceps , motor unit recruitment , electromyography , anatomy , medicine , physical medicine and rehabilitation , biomedical engineering
The maximum number of different motor unit action potentials (MUAPs), their firing rates, and total MUAP spikes/second recorded by monopolar needle electrode were determined for the biceps brachii muscle during 45‐degree elbow flexion. There were 4.2 ± 1.6 different MUAPs exceeding 100 μV. Mean firing rate was 10.0 ± 1.7 Hz, and total MUAP spikes/second were 40.3 ± 18. Recordings from 16 patients with neurogenic atrophy (NA) and just detectable weakness revealed corresponding values of 3.1 ± 1.7 different MUAPs, a mean rate of 10.2 ± 1.5 Hz and 30.6 ± 19 total MUAP spikes/second, not different from normal. In these patients, increased force of muscle contraction was required to activate high threshold motor units firing at high rates. In each of 4 patients just able to hold the arm against gravity, 1 or 2 “overdriven” motor units firing at a mean rate > 20 Hz were recorded. In 8 patients with myopathy and just detectable weakness, > 100 total MUAP spikes/second were recorded. Antigravity posture as a reference level of innervation has the advantage that motor unit firing rate is set about that of physiologic tremor (10–13 Hz). Its application was helpful in quantifying recruitment.